1. Field of the Invention
The present invention relates to an electromagnetic actuator, such as a linear motor or the like, including a stator and a movable element, an exposure apparatus including the electromagnetic actuator, a device manufacturing method using the exposure apparatus, a device manufacturing factory in which the exposure apparatus is installed, and a method for performing maintenance of the exposure apparatus.
2. Description of the Related Art
Typical conventional exposure apparatuses used for manufacturing various devices, such as semiconductor devices, are step-and-repeat-type exposure apparatuses (also called “steppers”) which sequentially expose a plurality of exposure regions on a substrate (a wafer or a glass substrate) with a pattern of an original plate (a reticle or a mask) via a projection optical system while moving the substrate stepwise, and step-and-scan-type exposure apparatuses (also called “scanners”) which repeat exposure and transfer on a plurality of regions on a substrate by repeating stepwise movement and scanning exposure. Since the step-and-scan-type exposure apparatuses use only light relatively close to the optical axis of the projection optical system by limiting the light beam by a slit, more precise fine-pattern exposure with a wider angle of view can be performed.
Each of these exposure apparatuses includes stage devices (a wafer stage and a reticle stage) for positioning a wafer and a reticle while moving them at a high speed. A linear pulse motor (a linear motor) using a Lorentz force is usually used for driving such a stage. By using a linear motor, a movable unit and a fixed unit of a stage are subjected to high-speed driving in a non-contact state, and very precise positioning can be performed.
Recently, the acceleration of the stage has increased in accordance with an increase in the speed of positioning processing (improvement of throughput). For example, in step-and-scan-type exposure apparatuses, the maximum acceleration of the stage now reaches values of 5×9.81 m/s2 (5 G) for reticle stages, and 1×9.81 m/s2 (1 G) for wafer stages. Furthermore, in accordance with an increase in the sizes of reticles and wafers, the mass of the stage is also increasing. Accordingly, the driving force defined by (the mass of a moving body)×(acceleration) becomes very large, resulting in an increase in the calorific value of a linear motor for driving a stage, and the influence of generated heat from the motor on its surroundings is causing a problem.
Conventionally, in order to suppress heat generation from a coil, a refrigerant is caused to flow in the vicinity of the coil. In a linear motor described in Japanese Patent Publication No. 2505857, cooling is performed by causing a refrigerant to flow within a member for supporting both ends of an armature coil. In a linear motor described in Japanese Patent Publication No. 2661092, it is intended to reduce heat conduction to a moving body by mounting a permanent magnet via a heat insulator. In the linear motors described in Japanese Patent Application Laid-Open (Kokai) Nos. 10-127035 (1998), 10-309071 (1998) and 11-122900 (1999), an armature coil is directly immersed in a refrigerant, in order to improve the cooling efficiency.
FIGS. 2 and 3 are cross-sectional views, each illustrating the structure of such a conventional linear motor. In FIG. 2, reference numeral 1 represents an armature coil of a linear motor. A bar-shaped supporting member 2 having an H-shaped cross section holds a plurality of armature coils 1 arranged in a direction vertical to the plane of FIG. 2. A refrigerant 3 flows within both side portions of the supporting member 2 in a longitudinal direction. A filler 4 covers the surfaces of the armature coils 1. A permanent magnet 5 forms a magnetic field for the linear motor. A yoke 6 provides a magnetic circuit with the permanent magnet 5 and a magnetic field generated by the armature coil 1. In FIG. 3, components having the same reference numerals as in FIG. 2 have the same functions. As shown in FIGS. 2 and 3, the armature coils 1 are cooled by the refrigerant 3 flowing within the supporting member 2 at both side portions. In the configuration shown in FIG. 2, by covering the entirety of the armature coils 1 with the supporting member 2, and inserting the filler 4 between the supporting member 2 and the armature coils 1 except for a portion near the refrigerant 3, heat conduction from the surfaces of the armature coils 1 to the outside of the linear motor is prevented. In the configuration shown in FIG. 3, two bar-shaped supporting members 2 support only both side portions of armature coils 1 arranged in a direction perpendicular to the plane of FIG. 3.
In the manufacture of semiconductor devices, in order to improve productivity, it is necessary to perform abrupt acceleration and deceleration when positioning a reticle and a wafer for exposure. In order to increase the thrust of a linear motor, serving as an actuator for the positioning, it is necessary to increase one of the volume of the entirety of the linear motor, the magnetic flux density of the magnet, and the current of the armature coil. However, since the volume cannot be increased due to a limitation in design, and there is a limitation in the magnetic flux density due to the physical properties of the magnetic material, the current of the armature coil must be increased. In this case, the thrust increases in proportion to the current, while heat due to copper loss is in proportion to the square of the current. Accordingly, the necessary cooling capability also increases. The heat transfer capability to the refrigerant at that time is determined by the contact area, physical properties (thermal conductivity, specific heat and specific gravity), the temperature difference and the flow rate. Since the contact area and the physical properties are determined by the structure and the material, the range of selection is small. Accordingly, it is necessary to increase the temperature difference between the armature coil and the refrigerant, or the flow rate of the refrigerant.
In the above-described conventional linear motors, since heat generated at the armature coil is not completely transmitted to the refrigerant, the surface temperatures of the armature coils and a jacket surrounding the armature coils are raised, thereby causing unevenness in the temperature of ambient air. Furthermore, in contrast to rotation-type motors, linear motors have a configuration in which at least a coil jacket must be exposed to air. In an environment requiring high precision for a semiconductor manufacturing apparatus or the like, since unevenness in the temperature of air degrades accuracy during a positioning operation, it is difficult to increase the thrust of a linear motor.
In linear motors described in Japanese Patent Application Laid-Open (Kokai) Nos. 10-127035 (1998), 10-309071 (1998) and 11-122900 (1999), in order to minimize the above-described temperature rise, armature coils are directly immersed in a refrigerant. In such a case, however, it is necessary to sufficiently insulate the armature coils, or use an insulating liquid as the refrigerant. If it is intended to increase the flow rate of the refrigerant in order to increase the cooling capability, since the resistance of a duct line increase as the flow rate increases, the pressure within the duct line increases. In order to reduce the resistance of a magnetic circuit, a thinner structure material for covering the surfaces of the armature coils is preferred. However, since a thickness sufficient enough to endure the pressure of the refrigerant is required in the above-described linear motors, there is the possibility that the thrust of the motor decreases in spite of the intension to increase it.